The present invention relates to a method and apparatus for irradiating fluoropolymer materials. It finds particular application in conjunction with the irradiation of polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and chlorotrifluoroethylene (CTFE) to degrade their mechanical properties. It is to be appreciated, however, that the present application is also applicable to the radiation treatment of other polymeric materials to alter chemical resistance, electrical properties, thermal stability, surface properties, and other characteristics.
Finally, milled PTFE is used as a common additive to inks and to lubricants. However, PTFE is an extremely tough material with very strong bonds. It is extremely difficult to mill into a fine powder.
In order to facilitate the milling process, radiation has been used to break chemical bonds in the PTFE polymer chains. In one technique, Teflon material was placed in open containers in a cobalt 60 (60Co) vault. Gamma rays from the cobalt 60 irradiated the PTFE for a duration which weakened the bonds sufficiently, typically on the order of several hours.
In another technique, PTFE material, in granules, sintered shavings, or other thin, small pieces was placed in an open tray. The tray was passed slowly through an accelerated electron beam irradiating the PTFE material. The product was raked or stirred and passed through the electron beam again.
These techniques have several drawbacks. First, a significant quantity of hydrogen fluoride (HF) gas is released into the atmosphere. Hydrogen fluoride is highly corrosive and toxic to workers in the environment. Other toxic and corrosive gases, including fluorene, are also released. Further, treatment of PTFE in open containers releases PTFE dust into the environment which settles on walkways and other surfaces. PTFE is an extremely slippery lubricant creating fall and other injury hazards to workers. Moreover, the PTFE dust in the environment can be breathed by the workers. The present invention contemplates a new and improved fluoropolymer material irradiations apparatus and method which overcomes the above referenced problems and others.
In accordance with one aspect of the present invention, a method of irradiating fluoropolymer materials is provided. Oxygen and oxygen containing gases are removed from an irradiation chamber. The chamber is irradiated with penetrating, ionizing radiation. The fluoropolymer material is passed through the ionizing radiation in the oxygen and oxygen containing gas depleted environment of the irradiation chamber.
In accordance with more limited aspects of the present invention, the gases removed from the irradiation chamber include air and water vapor.
In accordance with a yet more limited aspect of the present invention, the irradiation chamber is evacuated.
In accordance with another more limited aspect of the present invention, the penetrating radiation is accelerated electrons.
In accordance with another more limited aspect of the present invention, the fluoropolymer material is in particulate form and the particles are rotated by magnetic or electrical fields.
In accordance with a yet more specific aspect of the present invention, irradiation of the fluoropolymer particles by the electron beam charges the dielectric fluoropolymer particles creating rotational forces.
In accordance with another aspect of the present invention, an apparatus is provided for irradiating fluoropolymer materials. A radiation source generates a beam of radiation which passes through an irradiation chamber. A vacuum pump draws down oxygen, oxygen containing gases, water vapor, and other gases from the irradiation chamber. A source of fluoropolymer materials supplies a fluoropolymer material to the irradiation chamber.
One advantage of the present invention is that it reduces the generation of toxic and corrosive gases.
Another advantage of the present invention is that it reduces and substantially eliminates the distribution of dust and toxic substances into the environment.
Another advantage of the present invention resides in improved worker safety.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.